Method of treating a cut edge and its adjacent portion in a porous sheet material



Jan. 16, 1968 H. A. RAUSING 3,364,050

METHOD O1" TREATING A CUT EDGE ANI) ITS ADJACENT PORTION IN A POROUS SHEET MATERIAL Filed June 22, 1964 United States Patent M 3,364,050 METHOD OF TREATING A CUT EDGE AND ITS ADJACENT PORTION IN A POROUS SHEET MATERIAL Hans Anders Reusing, Lund, Sweden, assignor to AB Tetra Pak, Lund, Sweden, 2 Swedish company Filed June 22, 1964, Ser. No. 376,803 Claims priority, application Sweden, July 1, 1963, 7,256/ 63 4 Claims. (Cl. 117-4) ABSTRACT OF THE DISCLOSURE A method to impregnate a laminated web of material which includes a paper layer to prevent wicking by the paper layer. An impregnating agent is applied to one surface of the web material and is pulled into and through the material by a suction source closely adjacent the other side of the material.

The present invention relates to a method of treating a cut edge and its adjacent portion in porous sheet material, for instance against capillary liquid absorption, particularly in a fibrous body layer in a laminate web having at least one fully covering outer layer of heatsealable plastic.

In the packaging industry the liquid absorption in cut edges in porous sheet materials has presented serious technical problems which have until now called for complicated solutions, all of which have aimed at sealing the cut edge and possibly the immediately adjacent portion of the sheet material.

An illustrative example of both the general problem and of some solutions resorted to is furnished by the increasingly common packaging system in which a web of packaging material is shaped into a tube by bending and uniting the edge, said tube having a longitudinal joint of the normal overlapping type and being supplied in its interior with a liquid to be packed and being divided into filled and sealed packages of cushion or tetrahedral shape by being sealed in narrow zones transversal to the tube axis. The web of packaging material generally consists of a fibrous body layer, for instance of paper, and a fully covering coating layer of a heat-scalable plastic applied to one side corresponding to the inside of the tube. This coating layer is liquid-proof and permits the tube to be sealed so as to form packages by means of pressure and supply of heat in the said zone. Also, the longitudinal overlapping joint of the tube between the web margins may be established by means of heatsealing the coating layers on one side of the web to the opposite side of the web. Along the interior web margin in the longitudinal joint of the tube one cut edge of the body layer faces the filling material, however. Depending on the nature of the body layer and the surface tension of the filling material, the filling material may be absorbed by capillary action through the cut edge in question, thus destroying the package wall material and/or destroying one of the sealing joints of the package.

In order to avoid these drawbacks it has previously been suggested that the otherwise exposed inner cut edge of the body layer in the package is covered or bridged during one of the phases of the packaging operation by a plastic strip uniting the coating layer in the final longitudinal joint on the inner Web margin with the coating layer on or in the immediate vicinity of the outer web margin. In addition it has been indicated as a solution that the body layer edge and the adjacent body layer portion of the inner web margin are impregnated with parai'hn or the like more or less from the cut edge 3,364,656 Patented Jan. 16, 1968 surface after establishing the cut edge. Whether this treatment takes place prior to or after the said coating layer has been applied to the body, the treatment has turned out to bring about an essential impairment of the adhesion between the body and the coating detrimental to the tightness and strength of the final package. In most cases the treatment merely implied immersion of the body edge into a melt, in which case the impregnation proper, i.e. the absorption of the impregnating agent, was unsatisfactory. This fact was particularly prominent when the treatment was carried out after the coating layer had been applied to the body.

The present process aims at eliminating these and other drawbacks and is essentially characterized in that the porous sheet material, before the said out edge is established, has an impregnating agent applied to it in a relatively low-viscosity form, eg parafiin in a melt, solution or suspension, in a zone divided by the corresponding cut line on one of its sides, preferably on its upper side, while in the corresponding zone on the opposite side it is subjected to such absorbing action that the impregnating agent is absorbed actively through the sheet material from the side on which it is supplied to the op posite side, whereupon excess agent, it any, is removed from the latter.

Further particulars and advantages of the invention will be apparent from the accompanying drawing showing an embodiment of the invention chosen by way of example and applied to a continuously running web of for instance paper.

In the direction of the arrow A a web 1 is led continuously beneath a nozzle 2 or the like which sweeps over a longitudinal zone 3 in which the web 1 is intended to be divided into two partial webs 5 and 6 by means of a longitudinal cut 4.

The nozzle 2 is continuously supplied with a lowviscosity impregnating agent, e.g. parafiin in a melt, solution or suspension, from a source not shown and applies the said impregnating agent to the upper side of the web I in the zone 3.

Beneath the web 1 there is a funnel-shaped suction box 7 resting with the edge of its widest end opening against the underside of the web 1. In the suction box 7 there is maintained, by means not shown and via its smaller end opening, a pressure below atmospheric. The suction box 7 is in such a position relatively to the nozzle 2 and the pressure below atmospheric in the suction box is adjusted in such a Way that the quantity of impregnating agent which is supplied to the upper side of the Web 1 by means of the nozzle 2 is absorbed through the web 1 so that the latter is impregnated with the agent in question in a through portion corresponding to the said zone 3. Excess volumes of agent 8, if any, are caught in the suction box 7 and are evacuated from the said box in order to be recirculated to the nozzle 2. In the drawing the excess quantity 8 is shown as being evacuated through the same line 9 by means of which the pressure below atmospheric is created in the suction box.

It has turned out that by correct adjustment of the supply of impregnating agent through the nozzle 2 and the suction action in the suction box 7 it is possible to bring about a local impregnation of the web 1 in the actual zone without any outer layer of the impregnating agent rising on either web side. This makes it possible to apply one or both web sides a layer consisting for instance of heat-scalable plastic and having an essentially even adhesion along the whole web width.

After the zonewise impregnation of the web 1 has been carried out, the web 1 is divided continuously according to the invention into the two partial Webs 5 and 6 by means of a longitudinal cut 4 essentially centrally of the zone 3. This slitting can be carried out by means known per se. It the partial webs 5 and 6 are to have a coating layer applied to either side, this application may take place either prior to or after the cutting but of course always after impregnation.

Above, the invention has been described with respect to a zonewise impregnation of a running web. However, the invention is also applicable to local impregnation in general of all kinds of porous sheet material where it is important that the cut edge in question is effectively sealed against liquid absorption through the cut edge.

What is claimed is:

1. A method of providing a laminated web material comprising the steps of: supplying a web of fibrous material, applying an impregnating agent to one side of said web in a narrow zone, applying suction pressure on the side of said web opposite to said narrow zone to pull said impregnating agent into said web, applying a coating of heat sealing plastic material to one side of said web and cutting said web through said narrow zone to provide a web material with an impregnated edge.

4 2. The method of claim 1 wherein said impregnating agent includes paraffin.

3. The method of claim 2 wherein said web is cut after the Web material has been coated With a heat seal- 5 able plastic material.

4. The method of claim 2 wherein said web is cut prior to the coating of the web material with a heat sealable plastic material.

ALFRED L. LEAVITT, Primary Examiner.

20 A. GRIMALDI Assistant Examiner. 

